Vibrating elements of said type are to be found particularly in loudspeakers of relatively small size, which are needed in large numbers for diverse electronic devices. With loudspeakers of this order of magnitude, plastic foils are predominantly used for the production of their diaphragms, wherein materials such as polycarbonate, polyarylate, polypropylene, polyethylennaphtalate, polyimide or even polyetherimide are used in material thicknesses of approximately 8 μm to 150 μm. Here it is pointed out that the list of usable plastics is not by any means complete and therefore the use of other materials is also imaginable. Frequently, a high-pressure deep-drawing method is applied herein, with which a plastic foil is heated up to the glass transition temperature of about 220° C. and is then pressed on a mold with a pressure of 20 bar to 25 bar. But, in principle, other drawing and stamping methods are also possible for the production of a diaphragm, particularly also those with a mold and a countermold.
Partly, so-called “bag diaphragms” are used, with which a recess is produced during the pressing process for the incorporation of a moving coil. The insertion of the coil takes place in such a way that the connecting leads lie on the upper side of the coil and are thus yet easily accessible even after the insertion. In quite a number of cases these connecting leads are led to the edge of the diaphragm and connected there to a housing of a loudspeaker, in which the vibrating element is used. This lead, which is, on the one hand, connected to the fixed housing, but, on the other hand, also to the moved vibrating element, leads to a number of problems besides having the advantage of a small electrical resistance:
The life span of the wire loop and its connections to fixed and moved parts is very limited, particularly with high amplitudes of the diaphragm.
The acoustic behavior of the vibrating element is considerably influenced by the wire loop. Apart from the fact that the diaphragm cannot completely swing freely due to the stiffness of the wire and the limiting frequency is thus very limited, each deviation of the wire loop from a predefined form leads to an influencing of a predefined vibrating and frequency behavior.
It should be taken care that the connecting lead does not touch the vibrating element or the loudspeaker housing at another place than the one provided for it, as this can lead to undesirable noise.
the wire loop even has an undesired self-resonant frequency.
the production process is comparatively complex, as the partly very thin wires must be led in a predefined way.
For this reason, diaphragms have already been used for some time, which diaphragms have electrically conductive areas in the form of a coating of an electrically conductive material. In addition, the coil wire is contacted with a conductive area in direct proximity of the coil and the connection to external connecting leads is accomplished by means of these conductive areas. This indeed reduces the problems mentioned above, but does not eliminate them completely. Moreover, the diaphragm at the contact points is stiffened by the necessary adhesive or solder joint, which again changes its acoustic characteristics. A further problem is the degradation of a conductive adhesive, which leads to strong resistance changes in the course of time.
Therefore, it is an object of the invention to provide a vibrating element with which said problems are avoided.